Biomechanical response of maxillary All-on-4 systems under different lateral occlusal guidance patterns: a three-dimensional finite element study
This three-dimensional finite element study demonstrates that canine-protected occlusion minimizes stress concentration on implants and abutments in maxillary All-on-4 systems across varying bone qualities, suggesting it offers superior biomechanical advantages over group function schemes despite increased framework deformation in lower bone density.
Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer
When a person loses all their teeth in the upper jaw, the path to rebuilding a full set of teeth is often complicated by the softness of the remaining bone and the presence of the large air-filled sinus cavity above the mouth. To solve this, dentists often use a technique called All-on-4, where four metal posts are screwed into the jaw to hold up a full arch of new teeth. Two of these posts are placed straight up, while the two at the back are tilted to avoid the sinus and grab onto whatever solid bone is available. Because these metal posts are fused directly to the bone without the cushioning shock absorbers that natural teeth have, every bite and every sideways grind sends force straight into the jaw. The big question for doctors is how to shape the biting surfaces of these new teeth so that they do not break or loosen the posts over time. Specifically, when a person moves their jaw to the side, should only the front canine tooth touch, or should several back teeth touch at once?
Researchers at the Affiliated Stomatological Hospital of Guizhou Medical University set out to answer this by building a highly detailed computer model of a human upper jaw. They started with a real, healthy volunteer who had a full set of natural teeth and a specific way of biting where the side teeth protect the back teeth during side-to-side movements. Using high-resolution scans of the volunteer's face and mouth, the team created a digital twin of the jaw, including the hard outer bone, the softer inner bone, and the nerves. They then digitally removed the natural teeth and replaced them with the All-on-4 system, placing four titanium implants and a bridge made of a strong metal framework topped with ceramic crowns.
To see how different biting styles would affect this system, the researchers simulated four distinct ways the teeth could touch when the jaw moved to the side. In the first scenario, only the canine tooth made contact, shielding the rest of the teeth. In the other three scenarios, the contact was shared: first by the canine and one back tooth, then by the canine and two back teeth, and finally by three back teeth with no canine involvement. They tested each of these four biting styles on three different types of simulated bone, ranging from dense and strong to soft and spongy, to see how the materials would react under pressure.
The computer simulation revealed that the way the teeth touch matters significantly for the health of the implants. When the bite was guided only by the canine tooth, the stress on the metal posts and the connecting parts remained lower and more evenly spread out. However, when the researchers allowed more back teeth to touch during the side movement, the stress on the implants increased sharply. In the simulations using the strongest bone type, the stress on the implant at the back of the mouth jumped by nearly forty-six percent when three teeth shared the load compared to when only the canine touched. In the most extreme case, the stress on the connector piece of the implant rose to nearly two hundred and sixty megapascals, a level that, while not causing immediate breakage, is high enough to wear down the metal over many years of chewing.
The study also showed that the quality of the bone changes how the entire structure behaves. When the bone was soft and spongy, the metal framework holding the teeth bent slightly more than it did in the strong bone. In fact, the framework bent almost fifty percent more in the softest bone condition when the back teeth were doing the guiding. This bending is a sign that the structure is flexing under the load, which could eventually lead to mechanical failures or discomfort for the patient. The researchers found that the parts of the bridge closest to the front of the mouth, specifically the connectors on the side where the jaw moves, consistently experienced the highest pressure, regardless of the bone type.
These findings suggest that designing the new teeth so that only the canine guides the side-to-side movement is mechanically safer for the All-on-4 system. This approach keeps the forces lower on the implants and reduces the amount the metal bridge has to flex. While the computer model was based on a single healthy person and does not account for every possible real-world complication like teeth grinding at night, the results provide a clear biomechanical reason to favor a canine-guided bite. For patients with weaker bone, this design choice might be even more critical, as it helps prevent the framework from bending excessively under the weight of daily chewing.
Drowning in papers in your field?
Get daily digests of the most novel papers matching your research keywords — with technical summaries, in your language.